1. Field of the Invention
The present invention relates to a barrier device for location in sewage systems, domestic waste pipes and the like, with the intention of denying rodents, such as rats, access to domestic buildings and other buildings through such sewage pipes. The barrier device is intended primarily to be placed in vertical sewage or waste pipes.
2. Description of the Prior Art
It is well known that the presence of rats in sewage systems gives rise to serious problems, both from a sanitory aspect and a technical aspect, and that these problems are greater in the large town or city environments, where the nutrient content of the sewage is particularly high. The sanitary problem resides in the access to domestic buildings, multi-unit dwellings, office blocks, storehouses, shops and other buildings available to rats through the sewage systems, primarily through the water closets, of such buildings. The technical problems reside, inter alia, in the damage created by rats gnawing at sewage pipes, resulting in leakages and, at times blockages As is well known, the front teeth of rodents grow at an average rate of 1 mm per month throughout the lifetime of the rodent. Consequently, the rodent is forced to gnaw, in order to maintain its teeth at a manageable length, and will gnaw on the most unlikely objects, even on cast iron pipes.
Laboratory studies and research, and also field research, have shown that rats are able to travel quite freely along sewage pipes, both vertically and horizontally extending pipes. In the case of vertical pipes, so-called downpipes or downcomers, rats are able to climb readily to heights of several stories in the case of multi-story buildings, provided that the internal diameter of the pipes are not greater than 110 mm, which is the pipe diameter most often used with downpipes fitted to multi-unit dwellings.
Detailed studies carried out, inter alia, with the aid of video film techniques which allow certain frequencies to be "frozen" or advanced slowly, have revealed valuable information concerning the climbing techniques of rats. When climbing up a vertical pipe, a rat will press its front and rear legs diametrically against the wall of the pipe to obtain climbing purchase. Large rats will also press their backs against the wall of a pipe, in order to obtain a better purchase. Thus, in order to be able to ascend a pipe, it is necessary for the rat to obtain support against the wall of the pipe. This means that a part of the rat's body will be located in the central region of the pipe as the rat climbs.
Several attempts have been made to prevent the migration of rats through sewage systems. One known example of a device constructed to this end comprises a balanced flap fitted to a sewage pipe, this flap being openable in the direction of sewage flow, but self-closing in the opposite direction. It has been found that rats have overcome this barrier, by mutually cooperating to put the mechanism out of action.
U.S. Pat. No. 3,741,590 teaches an arrangement which is said to prevent rodents climbing up downpipes. The inventive arrangement described in this publication has a conically flared section located in the waste pipe. According to the specification, an incoming pipe section is extended down into the conically flared section, so that no deposits from the sewage will form on the surfaces of said section and therewith deny the rats a foothold on the wall surfaces thereof. In order to prevent rats from using the lower conical part of the flared pipe section as a jumping-off point and therewith reach the incoming pipe section, the latter is provided with a toothed lower edge. However, despite this arrangement, it was found that at least one rat had been successful in climbing further up the downpipe, assisted by other rats which positioned themselves in zig-zag fashion along the flared pipe section.
Although other rodent barriers have been tried, none has been truly successful. These earlier barriers have include the arrangement of a very deep water-seal, so configured as to make it difficult for a rat to climb up the sides of the seal or to swim through the same. However, rats have still been successful in penetrating such barriers, despite their ingenuity. It may also be difficult to position a water-seal, and the provision of such a water-seal may cause problems relating to the flow of water in and the hydraulic function of the sewage system.
A common feature of the aforementioned rodent barriers is that they must be built into sewage pipe or conduit when installing said pipe or conduit and that they can only be installed in existing pipes, etc, with great difficulty. Furthermore, because of their wide diameters, the known rodent barriers are much too large to be accommodated in normal pipe channels preformed in existing buildings.
The object of the present invention is to provide a rodent barrier arrangement which can be mounted in both new sewage pipe installations and in existing, older sewage pipe installations. The arrangement is intended to effectively bar the passage of the common sewer rat and also the larger rat which has recently begun to habit sewage systems in which the sewage has a plentiful supply of nutrient. The characteristic features of the present invention are set forth in the following claims.